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“Raft” Formation by Two-Dimensional Self-Assembly of Block Copolymer Rod Micelles in Aqueous Solution


  • We thank the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT), the Centre for Self-Assembled Chemical Structures (CSACS), and the National Sciences and Engineering Research Council of Canada (NSERC) Discovery grant for financial support. Thanks are also due for the block copolymer sample PEO45-b-PCL18, which had been prepared by Dr. Tony Azzam in connection with earlier work.


Block copolymers can form a broad range of self-assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free-standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core-crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)-block-polycaprolactone in water, co-assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one-dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.